The present invention relates to the technical field of a vacuum booster that uses vacuum to boost an input by a predetermined servo ratio and generate a large output, a brake system that is equipped with the vacuum booster as a brake booster, and a method of manufacturing a plate plunger that is used in a vacuum booster and determines a predetermined servo ratio together with a reaction disc. In the description of the specification of the present invention, front-and-rear direction relationships will be described with “front” representing the direction in which an input shaft moves when the vacuum booster is operative and “back” representing the direction in which the input shaft returns when operation is cancelled.
In brake systems of automobiles such as passenger cars, many vacuum boosters that use vacuum to boost an input by a predetermined servo ratio and generate a large output are used. As such vacuum boosters, many vacuum boosters in which the predetermined servo ratio is set by a reaction disc and a plate plunger are known (e.g., see JP-A-63-269768).
FIG. 4 is a longitudinal sectional view showing a vacuum booster described in JP-A-63-269768. In FIG. 4, 1 is the vacuum booster, 2 is a shell that forms a predetermined interior space, 3 is a valve body that is partially and air-tightly disposed in such a way as to be capable of sliding inside the shell 2, 4 is a power piston that is disposed between the shell 2 and the valve body 3 and air-tightly partitions the interior space of the shell 2, 5 is a constant pressure chamber that is demarcated by the power piston 4 and to which vacuum is always introduced, 6 is a variable pressure chamber that is demarcated by the power piston 4 and to which vacuum is introduced when the vacuum booster 1 is not operative and to which atmosphere is introduced when the vacuum booster 1 is operative, 7 in an input shaft to which an input is applied from the outside, 8 is a valve plunger that is supported in such a way as to be capable of sliding in the valve body 3 and is operated by the input shaft 7, 9 is a vacuum valve seat that is disposed in the valve body 3, 10 is an atmosphere valve seat that is disposed in the valve plunger 8, 11 is a valve element that is disposed in the valve body 3 and is disposed in such a way as to be capable of being seated in and unseated from the vacuum valve seat 9 and the atmosphere valve seat 10, 12 is a control valve comprising the vacuum valve seat 9 and the atmosphere valve seat 10 and the valve element 11, 13 is a vacuum introduction passageway that introduces vacuum to the variable pressure chamber 6 through the constant pressure chamber 5, 14 is an atmosphere introduction passageway that introduces atmosphere to the variable pressure chamber 6, 15 is an output shaft that is air-tightly disposed in such a way as to be capable of sliding in the shell 2 and outputs to the outside because of the operation of the power piston 4, 16 is a disc-shaped reaction disc that is pushed by a reaction force from the output shaft 15 and elastically deforms when the vacuum booster 1 is operative, 17 is a plate plunger that is supported in such a way as to be attachable to and detachable from the valve plunger 8 and with which the reaction disc 16 that has elastically deformed comes into contact, 18 is a return spring that always energizes the valve body 3 in the inoperative direction, and 19 is a vacuum introduction port that introduces vacuum to the constant pressure chamber 5.
This conventional vacuum booster 1 is used as a brake booster in a brake system shown in FIG. 5, for example. In FIG. 5, 20 is the brake system, 21 is a brake pedal that operates the input shaft 7 of the vacuum booster 1, 22 is a tandem master cylinder that is operated by the output of the vacuum booster 1, 23 is brake cylinders that generate brake force, and 24 are wheels.
The operation of the vacuum booster 1 and the brake system 20 of the conventional example will be described.
When the brakes are inoperative, the vacuum booster 1 is in the inoperative state shown in FIG. 4 and the input shaft 7 is in a backward limit position. Further, normally, a predetermined vacuum is being introduced to the constant pressure chamber 5 through the vacuum introduction port 19. Additionally, in the inoperative state of the vacuum booster 1, the valve element 11 is seated in the atmosphere valve seat 10 and unseated from the vacuum valve seat 9. Consequently, the control valve 12 places the variable pressure chamber 6 in communication with the constant pressure chamber 5 via the vacuum introduction passageway 13 and cuts off the variable pressure chamber 6 from atmosphere. Because of this, vacuum is also being introduced to the variable pressure chamber 6. Moreover, the reaction disc 16 and the plate plunger 17 are apart from each other.
When the brake pedal 21 is depressed, the input shaft 7 moves forward and the valve plunger 8 moves forward. When this happens, the valve element 11 becomes seated in the vacuum valve seat 9, and the atmosphere valve seat 10 moves away from the valve element 11. That is, the control valve 12 cuts off the variable pressure chamber 6 from the constant pressure chamber 5 and places the variable pressure chamber 6 in communication with atmosphere via the atmosphere introduction passageway 14. Consequently, atmosphere (air) is introduced to the variable pressure chamber 6 and a pressure difference arises between the variable pressure chamber 6 and the constant pressure chamber 5. Because of this pressure difference, the power piston 4 operates and causes the valve body 3 to move forward counter to the energizing force of the return spring 8. The reaction disc 16 and the output shaft 15 move forward because of the forward movement of the valve body 3, and the vacuum booster 1 operates. The forward movement of the output shaft 15 causes unillustrated pistons of the master cylinder 22 to move forward. However, the master cylinder 22 substantially does not generate hydraulic pressure because of the loss stroke of the brake system 20. At this time, the pedal force of the brake pedal 21—that is, the input of the vacuum booster 1—is small, and the reaction disc 16 and the plate plunger 17 are not in contact with each other.
When the pedal force—that is, the input of the vacuum booster 1—increases until the loss stroke of the brake system 20 ceases, the master cylinder 22 generates hydraulic pressure. The brake cylinders 23 generate brake force because of the hydraulic pressure of the master cylinder 22, and brakes are applied to each of the wheels 24.
Meanwhile, a reaction force is transmitted via the output shaft 15 to the reaction disc 16 by the hydraulic pressure of the master cylinder 22. For this reason, the reaction disc 16 elastically deforms and expands toward the plate plunger 17. Additionally, when the input applied to the input shaft 7 increases to a predetermined magnitude, the elastically deformed reaction disc 16 comes into contact with the plate plunger 17. Because of this, the reaction force is transmitted via the plate plunger 17, the valve plunger 8, and the input shaft 7 to the brake pedal 21, so the driver becomes aware of the operation of the brakes.
In this way, the vacuum booster 1 substantially does not output with respect to the input (pedal force) while the reaction disc 16 is not in contact with the plate plunger 17 and substantially outputs when the reaction disc 16 is in contact with the plate plunger 17. At this time, as shown in FIG. 6, the output of the vacuum booster 1 jumps in to a predetermined magnitude.
While the vacuum booster 1 is in operation, the valve body 3 moves forward, so the valve element 11 gradually approaches the atmosphere valve seat 10. Additionally, in the intermediate load state before the variable pressure chamber 6 reaches atmospheric pressure, the valve element 11 is seated in both the atmosphere valve seat 10 and the vacuum valve seat 9, and the control valve 12 enters a balanced state in which it cuts off the variable pressure chamber 6 from both the constant pressure chamber 5 and atmosphere. In this balanced state, the output of the vacuum booster 1 becomes an output in which the input has been boosted by the servo ratio. That is, as shown in FIG. 6, in the intermediate load state after the jump-in, the vacuum booster 1 exhibits an input/output characteristic that becomes an output in which the input has been boosted by a servo ratio SR. In that case, the servo ratio SR is given by the ratio of the area of contact between the output shaft 15 and the reaction disc 16 with respect to the area of contact between the plate plunger 17 and the reaction disc 16.
When the brake pedal 21 is released, the input shaft 7 moves backward, the vacuum valve seat 9 moves away from the valve element 11, and the atmosphere valve seat 10 becomes seated on the valve element 10. When this happens, the air that was introduced to the variable pressure chamber 6 flows to the constant pressure chamber 5 via an opening between the vacuum valve seat 9 and the valve element 11 and the vacuum introduction passageway 13, and the air that has flowed to the constant pressure chamber 5 flows out from the constant pressure chamber 5 through the vacuum introduction port 19. Because of this, the pressure in the variable pressure chamber 6 drops, and the power piston 4, the output shaft 5, the valve body 3, the reaction disc 16, the plate plunger 17, and the valve plunger 8 move backward because of the energizing force of the return spring 18. When this happens, the pistons in the master cylinder 22 also move backward and the hydraulic pressure in the master cylinder 22 gradually drops and ceases. Additionally, the valve body 3 and the valve plunger 8 are regulated in their backward limit positions, the vacuum booster 1 enters the inoperative state shown in FIG. 4, and the brakes of the wheels 24 are released.
When the variable pressure chamber 6 reaches atmospheric pressure when the vacuum booster 1 is operative, the vacuum booster 1 reaches a full load state that becomes an output in which the input is not boosted by the servo ratio SR.
There has been proposed a vacuum booster which, by fitting and supporting the plate plunger 17 in the valve plunger in such a way as to be attachable thereto and detachable therefrom and giving the shape of the portion of the plate plunger 17 that comes into contact with the reaction disc 16 the shape of a projection or the shape of an inclined surface, makes the servo ratio SR and the jump-in amount in the input-output characteristic line diagram of the vacuum booster 1 changeable in a variety of ways and can suitably accommodate different input/output characteristics of vacuum boosters (see Japanese Patent No. 2,959,585). The reference signs used for the configural elements are not the reference signs given in JP-A-63-269768 and Japanese Patent No. 2,959,585.